Atmospheric-pressure plasma etching of gallium nitride (GaN) substrate using hydrogen radicals instead of chlorine radicals was investigated toward the backside thinning of GaN vertical power devices to reduce on-resistance. As a basic experiment, a pipe-shaped electrode was placed facing the GaN substrate to generate atmospheric-pressure plasma of a gas mixture of helium and hydrogen, and high-speed etching of approximately 4 μm/min was achieved. Although many spherical Ga metal particles were observed on the surface after processing, the addition of oxygen gas was found to be able to suppress them.

In addition to silicon carbide (SiC) and gallium nitride (GaN), gallium oxide (Ga2O3) is attracting attention as a widegap semiconductor material. Ga2O3, unlike SiC and GaN, is not as hard, but has strong cleavage properties, making highly effective mechanical machining difficult. Thus, the processing of Ga2O3 by high-speed etching employing atmospheric-pressure plasma was studied. An extremely high removal rate of 60 μm/min was obtained due to basic processing experiments using hydrogen gas instead of toxic and corrosive chlorine gas as the reaction gas.